1. Field of the Invention
The present invention relates to a projection image display device that enlarges and projects an image displayed on a reflective light valve onto a screen, and more particularly, to a single projection display device that has high portability and can be held in one hand.
2. Description of the Related Art
In recent years, there has been a demand for projectors including a handheld-type single projection display device having high portability.
Particularly, among the handheld-type projectors, a projector that is sufficiently small so as to be held in one hand, like a flashlight or a penlight, and can project an image on a desired place (for example, a wall or a ceiling) is convenient.
A reflective light valve, such as a reflective liquid crystal device (LCOS) or a DMD (digital micro device), has been known as a light valve that has been used for the projector. The reflective light valve can increase an aperture ratio, as compared to a transmissive light valve, and can meet demands for high resolution and high illuminance. In addition, the reflective light valve can facilitate a reduction in the size of a device.
As the reflective liquid crystal display device capable of improving the portability of a device, for example, a projection display device shown in FIG. 6 has been proposed which uses a so-called color quad (an optical system obtained by combining a wavelength-selective polarization rotator that rotates polarized light in a predetermined wavelength band and a PBS prism) 460 and three reflective liquid crystal display devices 424a, 424b, and 424c to project an image onto a screen through a projection lens 426 (this type of projection display device is disclosed in JP-A-2001-281614).
For example, a single projection display device shown in FIG. 7 has been proposed which uses one reflective liquid crystal display device 524 and a polarizing prism 514 having a polarized light separation plane 516 to project an image onto a screen through a projection lens 526 (this type of projection display device is disclosed in JP-A-2001-201793).
However, of the projection display devices according to the related art, the projection display device shown in FIG. 6 (for example, JP-A-2001-281614) includes three light valves, which are the reflective liquid crystal display devices 424a, 424b, and 424c, and uses a so-called color quad 460. Therefore, the width of an intermediate part between the front part including a light source unit 401 and an illumination optical unit (which includes, for example, a fly-eye 406, a comb type filter 408, and a field lens 410) and the rear part including the projection lens 426 is significantly increased, which makes it difficult to significantly reduce the size of a device. Therefore, the projection display device is not suitable for a straight type device that is sufficiently small to be held in one hand, such as a flashlight or a penlight.
Of the projection display devices according to the related art, the projection display device shown in FIG. 7 (for example, JP-A-2001-201793) includes a single light valve, which is the reflective liquid crystal display device 524, but the optical axis X1 of a light source unit 501 and an illumination optical unit (which includes, for example, a fly-eye 506, a comb type filter 508, and a field lens 510) is bent at a right angle with respect to the optical axis X2 of the projection lens 526 in the polarized light separation plane 516. Therefore, the projection display device is not suitable for a straight type device that is sufficiently small to be held in one hand.